As emphasis shifts to greater use of LNG as an environmentally "green" fuel, the need for free-standing dispensing stations grows. Currently LNG is primarily used for industrial applications, or long term storage of natural gas in liquified form as a space conservation measure. While popular, LNG or propane tank fueling for home, cabin or camp use is still, volumetrically, less than half of all usage.
A major foreseeable growth area is in vehicular use, particularly in mass transit and fleet truck and/or utility van usage. Personal automotive use is still some way off, but promises to become significant as auto emissions reduction target dates approach.
Portable LNG "stations" consisting of a storage tank module (including a valve box) and an associated pumping module or skid have recently become available. These are used at various new field sites, either temporarily until a permanent station with underground tank storage is built, or until the particular job at that site is completed. Examples include industrial or utility vehicle field stations at remote job sites, at airports or where demand requires, e.g. at an industrial plant or vehicle depot when a vehicle fleet or plant operation is converted to LNG fuel.
However, such stations today are manually operated by authorized "station" operator or driver personnel, and have, at best, rudimentary leak detection systems. They are limited in usage in that the filling of the storage tanks is not remotely monitorable at a central station, nor is the dispensing monitorable or subject to charge pre-authorization, monitoring or control. The safety status is not remotely monitorable or controllable for shut-down during emergency or unauthorized usage.
One very serious problem with attendant-less refueling stations is security. The product is expensive and valuable, such that there is a need for accurate tracking of both filing (independent of the supplier's truck in order to verify filling quantities and charges), and user pumping (for full billing to the customer). Thus security is needed for authorized access to both fill and pump to prevent cheating upon filling and theft upon customer use. In addition, the product is a fuel with attendant fire and explosion hazards such that unauthorized use could lead to safety hazards, e.g. deliberate or accidental discharge by unauthorized persons.
A number of U.S. patents have been directed to a variety of detection systems for gas or fluid flow, including: Massa U.S. Pat. No. 4,066,095; Slocum et al., U.S. Pat. No. 4,736,193; Andrejasich et al., U.S. Pat. No. 4,835,522; Furuyama U.S. Pat. No. 4,752,698; and Slocum U.S. Pat. No. 4,740,777. None of these address the special problems of portable field LNG storage/dispensing stations.
Accordingly, in order to facilitate the use and expand access to meet customer usage requirements, there is a need for specially adapted systems to remotely monitor and control operations at attendantless free-standing LNG field stations, and to permit user card-controlled access payment and dispensing 24 hrs/day while maintaining a high degree of security and the ability to remotely change security access codes in real time as safety and customer needs require.
Such a system needs to be: remotely controllable via a wireless communications link; have the ability to monitor day to day usage; inventory the remaining supply and signal refilling as demand varies; authorize, restrict and control access; provide field condition instruction and use instructions; sense dangerous operations including leak detection; keep a history of transactions and inventory; and signal and control operations, including shut-downs or shut-offs during emergency conditions.